Method of quenching slag

ABSTRACT

A METHOD OF REDUCING HYDROGEN SULFIDE EMISSION DURING THE QUENCHING OF HOT BLAST FURNACE SLAG. MORE PARTICULARLY, THE ADDITION OF AN ALKALI OR ALKALINE EARTH METAL OR ALUMINUM OXIDE OR CARBONATE TO THE WATER USED TO QUENCH MOLTEN BLAST FURNACE SLAG IS FOUND TO REDUCE HYDROGEN SULFIDE EMISSION.

United States Patent 3,758,292 METHOD OF QUENCHING SLAG John B. Kuntz,Monroeville, and Anthony A. Spinola, Penn Hills Township, AlleghenyCounty, Pa., assignors to United States Steel Qorporation N0 Drawing.Filed May 21, 1971, Ser. No. 145,966

Int. Cl. C21b 3/08 U.S. C]. 75-24 5 Claims ABSTRACT OF THE DISCLOUREBACKGROUND OF THE INVENTION Blast furnace slag, depending upon itschemical composition and the physical form in which it is permitted tosolidify, has many uses. Three general physical types are produced bydifferent methods of cooling from the molten state, i.e. air-cooled,granulated, and expanded. Air-cooled slag, the crushed slag of commerce,is prepared by pouring the molten slag onto a slag bank or into a pitwhere it is allowed to solidify. Granulated slag is prepared by threegeneral methods: pit, jet or dry granulation. Pit granulation consistsof running the molten slag directly into a pit of water. In the jetprocess, the molten stream of slag is broken up by a high-pressure waterjet as it falls into the pit, and the granulated slag falls into thewater in the pit to be further quenched. Dry granulated slag is made ina mechanical device using small amounts of water. Expanded orlightweight slag is the foamed product produced when hot slag isexpanded by applying a limited quantity of water or a combination ofwater and air or steam.

In each of the above processes, with the exception of the first, wateris used to quench the hot slag. The contact of the hot slag with thecooling water produces steam which along with volatile matter formedduring the quenching operation escapes into the atmosphere, in someinstances causing severe pollution problems. One of the more insistentpollutants produced in the quenching operation, detectable in extremelylow concentration in the atmosphere, is hydrogen sulfide, H S. Althoughthe reactions which result in the formation of H 8 are not fullyunderstood, they are believed to be between sulfur compounds in the hotslag and water.

Larger quantities of hydrogen sulfide are evolved when the slag is at ahigh temperature; however, even at the relatively low temperatures whichair-cooled slag may reach after a period at the slag site, the merecontact of moist air or rain with the cooled slag will evolveappreciable quantities of hydrogen sulfide.

Thus, there exists a need to provide a method of quenching hot slagwhereby the evolution of volatile materials, especially hydrogensulfide, which are generated during the quenching operation is reducedor eliminated. It is an object of this invention to provide such amethod.

SUMMARY OF THE INVENTION Accordingly, we have discovered a method ofreducing the evolution of hydrogen sulfide normally generated during thequenching of slag by quenching the hot slag with an aqueous solutioncontaining an anti-emission agent which preferentially reacts with thesulfur compounds in the slag, thus effectively preventing or reducingthe formation of hydrogen sulfide. The anti-emission agents 3,758,292Patented Sept. 11, 1973 of our invention are alkali and alkaline earthmetal and aluminum oxides and carbonates.

DETAILED DESCRIPTION In our process, the anti-emission agent selectedfrom the alkali and alkaline earth metal and aluminum oxides andcarbonates is added to the water to be used to quench the slag. Theaddition may be done in any suitable way. If a solid anti-emission agentis used, it may be first dissolved in a small quantity of water and thenadded to the main water supply in the necessary amount, or it may beadded directly to the water supply in solid form. If a liquidanti-emission agent is used, it may be added to the quench water at anytime prior to use. Preferably, it is added just prior to use by meteringit into the water stream as it flows through a pipe.

No changes in the ordinary quench procedure are necessary. The onlydifference is the use of a Water solution of an anti-emission agent inplace of water. The same amount of water ordinarily used is used in ourprocess.

The quantity of hydrogen sulfide evolved is dependent upon the initialtemperature of the slag, the sulfur content of the slag (typicallybetween 0.75 and 2.25 percent by weight), and the final temperature.Where the initial 0 temperature of the slag is about 2200-2400 F., thesulfur content is in the typical range and the final temperature is ator slightly above ambient, hydrogen sulfide emission is in the range of10,000 to 20,000 parts per million (p.p.m.) by volume. A generallyuseful anti-emission agent should lower the hydrogen sulfide emission toa maximum of about 500 p.p.m.

The anti-emission agents of our invention are the alkali and alkalineearth metal and aluminum oxides and carbonates. Preferred agents arealuminum oxide, calcium oxide and sodium carbonate. The aqueous solutionof the anti-emission agent is the quench-anti-emission medium. Bestresults are obtained when the concentration of the anti-emission agentin the quench water is at least 3 percent by weight. However,satisfactory results are also obtained using saturated solutions ofthose anti-emission agents which are only slightly soluble in Water, asfor example, Al O' Although we have not confirmed the mechanisminvolved, we believe that our anti-emission agents prevent the emissionof hydrogen sulfide by reacting with the hydrogen sulfide that is formedupon contact of the slag and water. It is postulated that ouranti-emission agents acting as bases neutralize the acidic hydrogensulfide to yield a soluble metal sulfide. Regardless of the mechanisminvolved, the anti-emission agents of our invention act to retard theemission of hydrogen sulfide thereby reducing the pollution normallyassociated with slag quenching operations.

The invention is further illustrated by the following example:

Example One hundred grams (g.) of blast furnace slag ground to minus 20mesh and containing about 1.35 weight percent sulfur was transferred toa graphite crucible. The crucible was placed in an electric furnacecapable of reaching a temperature of 2500 F. The furnace was thenflushed with argon to provide an inert atmosphere and thereby preventthe formation of oxides of sulfur.

To quench the hot slag a quick sealing reaction chamber was designed.The reaction chamber consisted of a 11.29 liter stainless steelcylinder, spraying apparatus for introduction of the quench medium, anda port for introduction of the slag. The chamber was air-tight.

The furnace was activated and the slag heated to the desired temperaturein the inert atmosphere. Concurrently, the reaction chamber and samplingsystems were evacuated. The sampling system was isolated from thereaction chamber which was opened to allow admittance of the slagsample. As the heated crucible containing molten slag was quicklyintroduced into the reaction chamber, an optical pyrometer reading ofthe temperature was taken. The chamber was sealed and after opening thevalve to the sampling system, the entire system was evacuated to 25 mm.mercury absolute.

The quench medium was applied to the slag as a fine mist through sprayapparatus. The gases evolved from the reaction passed through aglass-wool demister screen to remove entrained water mist. When the slagsurface temperature reached about 200 F., the sampling valves on the gassample tube were opened and the gases were passed to the chromatographfor analysis.

Table I tabulates the results obtained using (1) various quench mediaand (2) diiferent slag temperatures at the moment of quench.

TABLE I Hydrogen Surface sulfide temperafanned, ture of percent Quenchmedia slag F.) by volume Test number:

1 Tap water 600 0. 0022 do 690 0.0025 3..- do 810 0. 0018 4 do 840 0.0024 5 do 1, 090 0. 0090 6 do 1, 550 0. 0090 7 do 1, 760 0.0072 8.... do2, 040 0. 2450 9 do 2, 280 1, 0290 10 Saturated aqueous 11. Saturatedaqueous A1203 2,400 0. 0059 12 3% aqueous NazCO; 2, 410 0. 0065 Theseresults show that when the aqueous solution of the anti-emission agentis saturated with said anti-emission agent or where the concentration ofsaid anti-emission agent is at least 3 percent by weight, the amount ofhydrogen sulfide emitted decreases at least 50 fold from the amountemitted when no anti-emission agent is present. This massive reductionin hydrogen sulfide emission is more than sufiicient in most cases tolower the emission to acceptable levels.

These results also show that when the slag temperature is relativelylow, the amount of hydrogen-sulfide emitted decreases. Thus, it ispossible, when using relatively cool slag such as air-cooled slag todecrease the concentration of the anti-emission agent below 3 weightpercent.

We claim:

1. A method of reducing the emission of hydrogen sulfide formed duringthe quenching of hot blast furnace slag comprising contacting the slagwith a quench-antiemission medium comprising an aqueous solution of ananti-emission agent selected from aluminum carbonates and oxides.

2. The method of claim 1 wherein the concentration of the anti-emissionagent is at least 3 percent by Weight.

3. The method of claim 1 wherein the anti-emission agent is aluminumoxide.

4. The method of claim 1 wherein the quench-antiemission medium is asaturated aqueous solution of the anti-emission agent.

5. The method of claim 1 wherein the anti-emission agent is aluminumcarbonate.

US. Cl. X.R.

